High-surface-area SmMn₂O₅ nanosheets with crystal orientation for propane combustion: A facile microwave-assisted hydrothermal method

SmMn₂O₅ nanosheets with high specific surface area and (0 0 1) facet orientation were synthesized by a facile and efficient microwave-assisted hydrothermal strategy. The BET surface area of the leaf-like mullite (SMO-MW) reached 122 m²/g, which was about 4 times to that of counterpart (SMO-HT) prepared by conventional hydrothermal method. The relative intensity ratio of (0 0 1) facet to (2 1 1) in SMO-MW was 0.74 ~ 0.87, which was higher than 0.23 ~ 0.28 in SMO-HT. Compared with SMO-HT, the Mn^x+ reduction temperature of SMO-MW declined significantly (ΔT = 63 °C for Mn⁴⁺→Mn³⁺, and ΔT = 76 °C for Mn³⁺→Mn²⁺) in the temperature-programmed reduction with H₂. Moreover, the weakened Mn-O bonds, higher concentration of Mn⁴⁺ ions, and more chemisorbed oxygen were obtained via microwave irradiation. The pre-exponential factors of SMO-MW reached about 9 times comparing with those of SMO-HT, revealing the generation of more active sites. Impressively, the MW-500 calcined at 500 °C exhibited high catalytic performance with a 50% C₃H₈ conversion at 243 °C, which was competitive with 1 wt% Pd/Al₂O₃ catalyst. Meanwhile, it kept above 90% propane conversion during 80 h durability test at 285 °C. This study was expected to promote a new strategy on developing efficient mixed oxides catalysts for environmental and energy applications.